Field
Apparatuses consistent with exemplary embodiments relate to illumination optical systems and three-dimensional (3D) image acquisition apparatuses including the same, and more particularly, to an optical system in which a field of illumination coincides with a field of view in order to obtain more precise depth information, and a 3D image acquisition apparatus including the optical system.
Description of the Related Art
Recent advances in 3D display apparatuses and an increasing demand therefore highlight the significance of 3D content in which depth can be perceived. Accordingly, research is increasing into 3D image acquisition apparatuses such as 3D cameras that enable users to create 3D content on their own. 3D cameras need to have a function through which both depth information and common 2D color image information are acquired through one photographing operation.
Depth information indicating distances between the 3D camera and surfaces of an object may be acquired using stereo vision methods that use two cameras, or using triangulation methods that use structured light and a camera. However, according to these methods, the greater the camera-to-object distance, the more imprecise the obtained depth information becomes, and these methods are highly dependent on the surface states of the objects being imaged. Thus, acquiring precise depth information with these methods is difficult.
To address these problems, Time-of-Flight (TOF) techniques have been introduced. TOF techniques measure a travel time of illumination light reflecting off an object after having been irradiated thereon to a light receiving unit for receiving the illumination light. TOF technology involves irradiating light having a specific wavelength (for example, near infrared rays having a wavelength of 850 nm) onto an object by using an illumination optical system that includes a light emitting diode (LED) or a laser diode (LD), receiving the light with a light receiving unit after the light is reflected off the object, and a series of process for extracting depth information, for example, by modulating the received light using a modulator with a known gain wavelength. Various TOF technologies for the series of processes are available.
In measuring distance using light reflected off an object after having been projected from an illumination optical system, the greater an amount of the reflected light that is incident on a 3D camera, the more precise the obtained depth information becomes. This is because in signal processing for extracting depth information using a 3D camera, a signal-to-noise ratio is proportional to an amount of incident light, and the greater the signal-to-noise ratio, the more precise obtained depth information becomes. However, in general, the field of view in a 3D camera does not match the field of illumination of its illumination optical system, and thus a considerable amount of illumination light may be lost and not used for extracting depth information. Therefore, an efficient optical system needs to be designed to provide a 3D camera with as much reflected light as possible.
In order for a 3D camera to obtain more precise depth information, a coherent light source having a short wavelength, such as an LD or an LED, may be used. However, when a coherent light source is used to emit light onto an object, speckle noise from the coherent light source may deteriorate the quality of the obtained image. To eliminate such speckle noise, a diffuser such as a frosted glass plate may be used. However, due to light scattering or absorption by the diffuser, depth information may be less precisely obtained.